camera: try to defer init of video objects

[KurtE]

This change, removes the automatic starting of the PWM clock on the GIGA, at startup. Instead it starts the clock if/when the sketch calls the Camera::begin method.

But to make this work, we also need to not start up the video objects, until after the MCLK has been started. We can do that with marking them as zephyr,deferred-init

This is to me a better solution to adding Portenta H7 than #184 as again this
only starts up (uses) the video resources IF you actually use them in your sketch.

Some of this is discussed in the Arduino discussion: zephyrproject-rtos/zephyr#93058 (reply in thread)

[mjs513]

@KurtE

Just incorporated this change inorder to test with the changes I am making to the ov7670.75 zephyr driver (see the pr) and it seems to working no issues so far.

I think I personally prefer doing it this way for a couple of reasons. Primary of which is that if there are any errors in the init function you have a better chance of seeing them when using the core vs having to keep compiling and testing directly in zephyr and then retest with the IDE. the other reason as you said is that you are only starting the camera if you are actually using the camera.

Fingers crossed that this change gets incorporated.

[KurtE]

@mjs513 Wondering if this will ever be reviewed, or maybe I should go ahead and close it out?

Personally I like the idea that the camera object is only initialized if/when a sketch uses the camera library. So for example
you don't have a PWM clock whirling around for a camera the does not exist and configure all of the DCMI pins.

Let alone it also enables you to use the Portenta H7 with cameras.

But just in case I just rebased it to the latest sources

[mjs513]

@mjs513 Wondering if this will ever be reviewed, or maybe I should go ahead and close it out?

Personally I like the idea that the camera object is only initialized if/when a sketch uses the camera library. So for example you don't have a PWM clock whirling around for a camera the does not exist and configure all of the DCMI pins.

Let alone it also enables you to use the Portenta H7 with cameras.

But just in case I just rebased it to the latest sources

@KurtE
I think I agree with you on this. When initialize something if you are never going to use your application.